Method of finishing gears



Jan. 29, 1935= R. s. DRUMMOND 1,989,651

METHOD OF FINISHING GEARS Filed April 11. 1932 5 Sheets-Sheet 1 INVENTOH ATTORNEYS Jan. 29, 1935.

R. s. DRUMMOND METHOD OF FINISHING GEARS Filed April 11, 1932 5 Sheets-Sheet 2 INVENTOR 205191-53 irzzzvzvwv J Jan. 29, 1%35.

METHOD OF FINISHING GEARS Filed April 11, 1952, 5 Sheets-Sheet 5 R. s. DRUMMOND 1,989,651

1935- R. s. DRUMMOND METHOD OF FINISHING GEARS Filed April 11, 1932 5 Sheets-Sheet 4 INVENTOR 254,56; S Irzzv77v/ a? BY 2 m W ATTO RN EY-S Jan. 29, 1935.

R. s. DRUMMOND METHOD OF FINISHING GEARS 5 Sheerls-Sheet 5 Filed April 11, 1932 INVE N TO R 3056f t S. lrzfzwzazm W/wmm A M WW/{5M ATTORNEYS Patented Jan. 29, 1935 UNITED STATES PATENT OFFICE Application April 11, 1932, Serial No. 604,575 In Great Britain August 17, 1931 19 Claims. (Cl. 51-278) The invention relates to the art of finishing gears and has for its object the correction of inaccuracies in form due either to original cutting or subsequent distortionduring heat treatment.

6 To this end the invention consists in the method and apparatus as hereinafter set forth.

In the drawings:

Figure 1 is a side elevation of one type of machine which is capable of use for carrying out my improved process;

Figure 2 is a plan view thereof;

Figure 3 is a sectional elevation showing the lap and the relative arrangement of the same with respect to the gear to be finished;

Figure 4 is a section through a portion of the gear and lap in engagement with each other;

Figure 5 is a similar view of a modified arrangement;

Figure 6 is a perspective view of the modified construction; v

Figure '7 is a vertical section through the construction shown in Figure 6;

Figure 8 is a sectional view illustrating the portion of the drive mechanism taken substantially on the line 8-8 of Figure 7;

Figure 9 is a horizontal sectional view taken substantially on the line 9--9 of Figure '1;

Figure 10 is a detailed view of a portion of Figure 6 with parts broken away;

Figure 11 is a diagrammatic sectional view through the oil pump;

Figure 12 is a diagram illustrating the manner of correcting the helical angle of a gear.

In the present state of the art it is quite com- I mon to finish gears by running them in mesh with a mating gear or lap and with abrasive material on the contacting surfaces. It is also old to impart-to the gear and lap a relative axial as well as rotatlve movement. The peripheral rotative speed is, however, usually considerably in execess of the speed'of axial reciprocation so that the path of movement of the abrading' particles is approxim tely parallel to the plane of rotation. Furthe v teeth of mating gears due'to rotation is zero at the pitch circle and progressively-increases as the point of contact moves away from the pitch circle, so that the abradi'ng action is unequal and tends to destroy the correct shape of the teetln ,r Lapping has also beenperformed by a rapid relative movement of the gear and lap axially while being slowly rotated, but as the direction of movement of theabrading particles is parallel to the successive lines of contact of the teeth upon each other, there is a tendency to form minute ore, the relative movement between. the

ridges on the tooth contours which interfere with smoothness of operation. A third method which has been used in gear lapping is by use of a lap in the form of a worm having the teeth thereof conjugate to the teeth of the gear to be lapped and in rotating the same in mesh with each other. This has the same objectionable features as the method described.

It is a primary object of the present invention to produce a relative movement between the surfaces of the gear and the lapping tool in a direction which 'is transverse both to the lines of simultaneous contact between the teeth of the lap and those of the mating gear and also transverse to the plane of rotation. This avoids on the one hand any tendency towards forming grooves or ridges in the contours of the teeth which are parallel either with the plane of rotation or lines of simultaneous contact and on the other hand avoids any changing of the lap from the correct form. To accomplish this transverse movement I employ a lapping tool having teeth that are conjugate to the teeth of the gear to be lapped but which have such angular relation to the axis of rotation that the axes of both gear and lap are non-parallel and have no common plane. Furthermore, the angle between the two axes must be' neither too large nor too small, but is within certain limits, such as three degrees and thirty degrees. For instance, if the gear to be lapped is a straight spur gear, the lap may be in the form of a helical gear having a helical an- .point contacts which generate an oblique line across the face of the spiral member.

Fractically, instead of a mathematical line the successive contacts will'be linesof limited length which generate a strip or band of contact the width of which depends upon the angular difference of the two axes. Thus as this angular difference is decreased, the width of the strip is enlarged and as the angular difference isincreased it is correspondingly narrowed. In addition to the rotation of the gear and lap about their respective axes, a relative feed movement is imparted in the direction of the axis of the gear. This movement is such as to extend the band of contact across the bearing face of the gear and this will generate I the complete contour of the tooth surface. However, the width of bearing'on the lap is not increased and therefore a very narrow lap may be successfully used in the process. but where. the width is greater the lap may be adjusted from time to time to bring a new portion of its surface into operation or if desired, the lap may be re-' ciprocated along its axis to spread the wear over an extended width.

A further feature of my improvement is that the lap may be formed from soft metal which can be easily and accurately machined to the correct form. It is necessary, however, to develop a pressure between the contacting surfaces of the lap and the gear which with one modification of my improvement is accomplished by forming the tooth thickness of the lap slightly greater than would be proper for a mating gear. This permits of crowding the teeth of the lap againstthe teeth of the gear soas to simultaneously lap the opposite faces of the gear teeth under any desired pressure of contact.

Instead, however, of developing the contact pressure as just described, it may be accomplished by forming the lap with a tooth thickness that is less than the interdental spaces in the gear prior to lapping and which therefore permits of placing the gear and lap in full mesh before the lapping operation. The lapping pressure is then ob-- tained by loading or resisting rotation of the driven member of the intermeshing gear and lap. This method has certain advantages over the method previously described as will be hereinafter set forth.

Thus far I have referred to the tool as a lap and the operation as lapping, but cefiain features of my invention have a broader application. 7 Thus with the tool having a hardened surface the operation may be that of burnishing and with a slightly modified construction the tool may operate to shave the surface of the gear to remove stock therefrom and to correct the form. Such modifications also come within the spirit of my invention.

Lapping In carrying out my invention as applied to lapping I first form a lapping member preferably of cast iron having teeth which areconjugate to the teeth of-the gear to be finished but which sustain such an angular relation'to the axis of rotation that the axes of the gear and iap will tie within the limits of three degrees ta thirty degrees and preferably from seven degrees to twenty degrees. setting of the axes ofthe gear and lap at such angle to each other with the result that when the gear andlap run in mesh the paths of contact thereon will be transverse to each other. Thus individual abrasive extended lines will action so that a coarse particle will not produce an extended mar in the finished surface.

Any suitable machine may be employed for mounting the gear and lap in operative relation to each other and for imparting thereto the required movement. As shown in detail in Figure 1, A is any suitable machine such as universal milling machine of ordinary construction which is provided with a work table B for supporting a work arbor C on which the gear D to be finished may be mounted. The table is raised or lowered by suitabie mwhanism (not shown) controlled by the handle E and the table B is moved longitudinally or parallel to the arbor Q lilili sh This will necessitate an accurate particles instead of generating. quickly pass into and out of.

the operation" of a handle F. There is also an adjustment operated by the handle G for moving the table inward or outward on the bed -G Above the table B is the arbor H having the lap I mounted thereon, said arbor being journalled bearings upon the adjustable slide J relatively movable in a direction parallel to the axis of the arb-or. The arbor H is driven by any suitable means such as the gearing K.

As shown in detail in Figure 3, the gear D to be lapped is detachably mounted upon the arbor C having a spl med or other driving engagement.

therewith and a clamping nut C' retains the work in position. Axial movement of the arbor is prevented by end thrust bearings C and (I on onposite ends of the bearing L. The lap I- may be of any desired dimensions but the teeth I thereof are so cut as to be conjugate to the teeth of the gear to be finished when its axis is arranged to be non-parallel to the axis of said gear and not in a common plane therewith.

In operation, assuming that the lap has first been formed as above described, it is mounted upon the arbor H while the gear D to be lapped is mounted upon the arbor C. The table B is then manually adjusted angularly so as to bring the teeth of the lap into parallelism with the teeth of the gear after which the table is vertically adjusted to intermesh the teeth or to place a predetermined contact pressure thereon. The abrasive compound is then spread on the surface by suitable means such as the tank N containing a suitable abrasive compound and into which a.

portion of the gear D dips. The operator then starts the machine which will cause the gear and lap to run in mesh, abrading the high points on the teeth or the gear until they approximate the true form. The lapping action is continuedwith suitable vertical adjustments of the table from time to time until the desired amount of stock has been removed. During the running at the gear and lap in mesh the table B is reciprocated i-ongitudinally by means of a handle F cr if desired by automatic mechanism, the amount of reciprocation being somewhat in excess at 'will be highly accurate and also be inexpensive as the lap can be easily and cheaply machined to the true form and constructed of inexpensive material such as east iron. thermore, by making the tooth cross section of the latter slightly in excess of that which would be proper for a mating gear, all backlash can be taken up and a cramping pressure placed upon the teeth. which it will be noted that each of the teeth I will have contact at two points, 1 and -2, with the intermeshing teeth of the gear on opposite sides of the interdental space. It .will also be noted that in the rotation of the lap and gear,

each of these points acts as a fulcrum to press the teeth against the other point plied pressure. Consequently, any desired pres= sure may be developed between the points or cone tact (which are of quite limited area) to pro-f ducethe desired abrading action and without materially increasing the reaction upon the arbors and their bearings. 'The actionis therefore quite different-from that illustrate-:1 in Fig Fur-- This is iliustrated in Figure 5 in with a multi are 4 where the teeth of the lap and gear contact on one side only of the interdental space.

In the modified construction illustrated in Figures 6 to 11 the machine is adapted to automatically perform the principal movements required. With this construction the lap I is mounted upon an arbor H journaled in bearings on heads H and H the latter being adjustable in ways H on the bed or frame of the' machine. The lap I can be axially moved by rotating the square shank Ci which carries at its opposite end the pinion Go (see Figure 10). The pinion G meshes with rack G on the sleeve G which in turn has a collar G abutting the lap 1. Thus upon rotation of the square shank G with a suitable handle the lap I and the arbor H on which it is mounted may be axially adiusted in the hearings on the heads H and H The arbor L on which the gear D to be lapped is mounted is carried by a carriage L mounted for transverse reciprocation on a cross head IF. This cross head is vertically adjustable on ways L on a column M extending upward from the base or frame M of the machine. The column M is also adjustable along segmental ways W on the bed M which are concentric with a vertical axis passing through the axis of the arbor H'. Thus by adjustingthe column M upon these segmental ways any desired angular relation may be established between the axes of the arbors H and L.

The arbor H is driven by suitable means such as a pulley and belt connection N from a drive shaft N actuated by the motor N the speed of rotation of said arbor being regulated through the medium of a reduction transmission gearing N Provision is also made for reciprocating the carriage L, this comprising a rack O on the carriage engaging a gear wheel 0' splined upon a vertical shaft 0 which is oscillated by a rock arm 0 connected to a link 0 engaging an adjustable throw crank O on a shaft 0 The shaft O is driven through the medium. of a reduction worm gearing 0" from the shaft N and the arrangement is such that a reciprocatory movement is imparted to the carriage L and arbor L simultaneously with the rotation of said arbor and gear D through the'actuation of the rotating lap I. The amplitude of movement is determined by the throw of the adjustable crank 0 which may be set according to the width of the gear which is lapped.

I To produce a proper lapping action, the contacting surface of the lap and gear must be pressed against each other with apredetermined pressure. Instead, however, of developing this pressure by crowing the teeth of the lap into pressure contact with both sides of the teeth of the gear as illustrated in Figure 5, the desired pressure is obtained by loading or retarding rotation of the gear. This has an important advantage in that the helical angle is maintained constant regardless of wear in the lap whereas with a construction where the axis of the lap ismoved towards the axis 'of the gear, wear will result in changing the helical angle.

To accomplish this purpose the lap is formedwith a tooth thickness which will fully enter the interdental spaces of the gear when the axes of said gear and lap are in the desired relation.

75 upon an adlustable tail stock L on said carriage closed valve Q. The pressure of the spring maybe varied by an adjusting screw Q so as to produce any desired resistance to the rotation of the pump and consequently to the rotation of the gear. The construction is such as to resist rotation of the gear in either direction. Thus in the operation of the machine the driving motor N is first operated in one direction for a sufficient length of time to properly lap the faces of the teeth on one side thereof and then by reversing the motor the opposite faces of the teeth are correspondingly lapped. In each instance the lag or resistance of the pump 1? will give a substantially constant pressure of contact between the teeth of the gear and those of the lap so as to produce a definite abrasive action.

In the manufacture of transmission gearings and also for other uses clusters of gears of different diameters are frequently formed integral.

with such. constructions the larger gear or gears" may form an obstruction to the lapping of the smaller gears. However, by modifying the lap such interference may be avoided. The several modifications which may be made are first, a decrease in the'diameter of the lap; second, in limiting the angular difference between the shafts of the gear and lap and third, by using only the portion of the lap adjacent to the 0bstruction.

My improved process of .lapping not only corrects tooth form but also corrects errors in indexing. This latter effect is facilitated by making the lap with a different number of teeth than the gear and preferably with a number which will cause a progression in the engagement of the gear teeth with those of the lap. Thus if the lap has one more or less tooth than the gear or than any multiple of the number of teeth of the gear, there will be a progression of one tooth with each cycle, thereby correcting any inaccuracies in indexing.

The lapping may be effected by the driving of either the lapping member or the gear, provided that the spiral angle of the driving .mem her is such as not to lie within the angle of friction. Thus in, a case where the spiral angle of one of said members does lie within the angle of friction it is necessary to apply the driving force to the other member.

While my improved process is applicable to the lapping of gears having any spiral angle to its teeth, it is also particularly applicable to the lapping of spur gears, the teeth of which have a zero spiral angle. For such use the lapping tool will have spiral teeth which are conjugate to the teeth of the gear and revolve about an axis which is non-parallel to the axis of the gear and does notlie in a plane common thereto.

My improved machine is also adapted for use in correcting various errors in gears aside from the tooth form. For instance. the tooth form of the gear may be correct but the gear may be slightly excentric on its axis so that the teeth on one side thereof are of greater radial distance .from this axis than onthe other side. Such defect is best corrected by adjusting the axes of the blank holding and lap holding arbors so as to crowd the tooth of the lap into contact with opposed surfaces of the interdental space in the gear as illustrated in Figure 5. Thus whenever a portion of the'gear of longer radius the pressure will be 1 ted comes into contact with the lap the lapping pressure will be increased so as to rapidly out down the surface of the tooth. On the other hand when the portion of the gear of shorterradius comes into intermeshing contact with the lap, reduced with less abrasive eflect. This action will therefore soon correct the gear of eccentricity.

Another error which may occur in gears that are of correct tooth form is a very slight error in helical angle. This will cause intermeshing gears to bear only at the ends of the teeth or one side or the gear instead of giving a distribug. To correct this defect the machine is adjusted so as to change the angle between the axes of the gear and lap slightly in excess of the amount of the error. For instance, as-

suming that the correct helical angle of theteeth is fourteen degrees and that upon testing the gear is found to have an angle of thirteen degrees, the machine may be set atan angle of fifteen degrees, after which the gear is further lapped. The result will be the correction of the gear more' rapidly than would be possible if the machine were set at the precise helical angle desired. This is for the reason that the high points will be more rapidly worn down and the bearing on the teeth shifted from the one end towards the center. It is not necessary that the lapping should be carried to an extent which would change the angle through the entire width of the tooth, for it is sufiicient to remove the high spots and the complete correction will then be eflected when the gears are even in service. diagrammatically illustrated in Figure 12, assuming that the line 33 is the helical angle of the tooth as first formed and the line 4-4 is the correct helical angle, the axes will be set so as to greatly exaggerated.

give a helical angle corresponding to the line 5-5. This will rapidly cut away the end portion 6 of the tooth so as to shift the bearing towards the center. It-is of course to be understood that the errors so corrected are very minute whereas the angles in the diagram are It is sometimes desirable to modify the form of gear teeth so as to give a slight relief on the addendum of each tooth. This may be accomplished by first lapping the gear with the axis of the gear and lap spaced from each other the correct distance corresponding to that of the meshing gears when in service and in then adiusting the axes slightly further apart and contimiing the lapping. This will have the effect of relieving the addendum a progressively increasing amount towards the outer end of the tooth.

While I have referred to the use of my method and apparatus for other operations than lapping, such as burnishing or shaving, these specific features will form the subject matter of other applications'for patent and will therefore not be described in detail. However, I have used the term finishing tool in the specification and claims as including within its meanng constructions capable of such analogous operations as burnishing and shaving.

For successful lapping of gears it is essential that there should be a carry-over of contact from tooth to tooth so that before one tooth of the lap separates from its contact with the tooth of the gear 'a succeeding lap tooth has come in contact with the gear tooth. The amount of this carryover may vary but is preferably equal to'at least construction of the gear to be ten per cent of the contact on each tooth. To accomplish this result it is frequently necessary to construct a lap having difierent characteristics from those of the mating gear. Thus in some instances there is no carry-over between the gear being lapped and its mating gear so'that the lap must be modified in oneor more of several ways. One modification is to increase the number of teeth in the lap relative to'those of the gear. Another mmification is to vary the helical angle so as to change the difierence in angle between the axes of the gear and lap within the limits of from three degrees to thirty degrees. A third modification is to increase the extent of the addendum of the lap teeth over that of the mating gear, this being possible by reason of the fact that it is customary to cut gears with a reater depth of interdental space thanthe actual contact bearing on the side of the tooth.

This application is a continuation inpart of my application Serial No. 547,704, filed June 29, 1931. Reference should also be made to my'copending application Serial No. 626,769, filed July 30, 1932 which shows and claims certain modifications of this invention.

What I claim as my invention is:

l. The method of correcting errors in helical angle of gears which consists in placing the gear in mesh with a lap having conjugate teeth, the axes of said gear and lap being non-parallel crossed at an angle less than 30 and having no common plane, and in adjusting one axis relative to the other through an angle in excess of the angle of error in said gear and lapping to rapidly cut down the high points.

2. The method of finishing gears which consists in running the gear to be finished in mesh with a lapping tool having conjugate teeth, the axes of said gear and lap being non-parallel, having no common plane and having a diiference in angle between the limits of three degrees and thirty degrees, said lap being modified in characteristics from those of the gear to be finished to increase the carry-over of the teeth thereof and in relatively' reciprocating said gear and lap in the direction of the axis of the gear.

3. The method of finishing gears which consists in running the gear to 'be finished in mesh with a iapping tool having conjugate teeth, the axes of said gear and lap being non-parallel, having no common plane and having a difierence in angle between the limits of thirty degrees, said lap being more of the characteristics of number of teeth, helical angle and extent of addendum of the teeth to increase the carry-over of said teeth and in relatively reciprocating said gear and lap in the direction of the axis of the gear.

4. A lap for finishing gears comprising a rotary member having conjugate teeth and modified from the structure of the gear to be finished to increase the carry-over of the teeth thereof.

5. The method of finishing gears comprising mating the gear member to be finished with a rotary finishing tool member having conjugate three degrees and I teeth, rotating one of said members thereby driving the other member through the intermeshing engagement of said teeth, the axes of said gear member and tool member lying in no common plane and being crossed at an angle such that the cross sliding motion during said rotation compensates for the excessive variation in the sliding motion due to the roll of said gears thereby obtaining a substantially uniform action over the of said gears thereby entire tooth height of the gear, and feeding one of said members relative to the other in the direction of the axis of said gear to be finished thereby distributing said uniform action over the bearing face of the gear.

6. The method of finishing gears comprising mating the gear member to be finished with a rotary finishing tool member having conjugate teeth, rotating one of said members thereby driving the other member through the intermeshing engagement of said teeth, the axes of said gear member and tool member lying in no common plane and being crossed at an angle less than twenty-five degrees and feeding one of said members relative to the other in the direction of the axis of said gear to be finished.

7. The method of finishing gears comprising mating the gear member to be finished with a rotary finishing tool member having conjugate teeth, rotating one through the intermeshing engagement of said teeth, the axes of said gear member and tool member lying in' no common plane and being crossed at an angle between three degrees and twenty degrees and feeding one of said members relative to the other in the direction of the axis of said gear to be finished.

8. The method of finishing gears comprising matingthe gear member to be finished with a rotaryfinishingtool member having conjugate teeth, rotating one of said members thereby driving the other member through the intermeshing engagement of said teeth, applying pressure to. to obtain pressure contact one of said members between the teeth of the driving and driven rnein-- bers, the axes of said gear member and tool member lying in no common plane and being crossed at an angle such that the cross sliding motion during said rotation compensates for the excessive variation in the sliding motion due to the roll obtaining a substantially uniform action over the entire tooth height of the gear, and feeding one of said members relative to the other in the direction of the axis of said gear to be finished thereby distributing said uniform action over the bearing face of the gear.

9. The method of finishing gears comprising mating the gear member to be finished with a rotary finishing tool member having conjugate teeth, rotating one of said members thereby driving the other member through the intermeshing engagement of said teeth, the axes of said gear member and tool member lying in no common plane and being crossed at an angle such that the cross sliding motion during said rotation compensates for the excessive variation in the sliding motion due to the roll of said gears thereby obtaming a substantially uniform actionover the gear, feeding one of 'tary lapping tool member having conjugate teeth,

applying a lapping compound to said teeth, rotating'one of said members thereby driving the other 1 member through the intermeshing engagement of said teeth, the axes of said gear to be lapped and said lapping tool lying in no common plane and of said members thereby driving the other member successively feeding being crossed at an angle less than twenty-five degrees, feeding one of said members relative to the other in the direction of the axis of said gear to be lapped and applying pressure to one of said members to obtain pressure contact between the teeth during the lapping action.

11. The method of lapping gears comprising mating the gear member to be lapped with a rotary lapping tool member having conjugate teeth,

applying a lapping compound to said teeth, rotating one of said members thereby driving the other member through the intermeshing engagement of said teeth, the axes of said gear to be lapped and said lapping tool lying in no common plane and being crossed at an angle from three degrees to twenty degrees, feeding one of said members relative to the other-in the direction of the axis of said gear to be lapped and applying pressure to one of said members to obtain pressure contact between the teeth during the lapping action.

12. The method of finishing gears comprising mating the gear member to be finished with a rotary finishing tool member having conjugate teeth, rotating one of said members thereby driv-- ing the other member through the intermeshing engagement of said teeth, the axes of said gear member and tool member lying in no common plane and being crossed at an angle less than 25, feeding one of said members relative to the other in the direction of the axis of said gear to be finished thereby extending the finishing action across the bearing face of the gear and feeding the axis of one member toward the axis of the other member until the desired size is obtained.

13. The method of finishing gears comprising mating the gear member to be finished with a rotary finishing tool member having conjugate teeth, rotating one of said members thereby driving the other member through the intermeshing engagement.of said teeth, the axes of said gear member and tool member lying in no common plane and being crossed at an angle between 3 engagement of said teeth, resisting the rotation of the driven member, the axes of said gear member and tool memberlying in no common plane and being crossed at an angle less than 25 and feeding one of said members relative to the other in the direction of the axis of said gear to be finished thereby extending the finishing action across the bearing face of the gear.

15. The method of finishing gears comprising mating the gear member to be finished with a rotary finishing tool member having conjugate teeth, rotating one of said members thereby driving the other member through the intermeshing engagement of said teeth, resisting the rotation of the driven member, the axes of said gear member and tool member lying in no common plane and being crossed at an angle between 3 and 20 and feeding one of said members relative to the other in the direction of the axis of said gear to be finished thereby extending the finishing actien across the bearing face of the gear.

16."The method of finishing gears comprising matingthe gear member to be finishedgwith a rotary finishing tool member havingiconjugate teeth, rotating one of said members thereby driving the other :member through the intermeshing engagement of said teeth, resisting the rotation of the'driven member; the axeg of said gear member and tool member lying inzno common plane and being crossed at an angle less than 25 and being spaced from each other to correspond with the axes of the gears when intrue mesh, feeding one of said members gelative to the other in the direction of the axis ef said gear to be finished, and then slightly separating said axes and further rotating said members while resisting the rotation of the driven member :to relieve the addendum of 7 each gear tooth.

17. The method of finishing gears having an adjacent obstructing member comprising mating the gear member to be finished with a rotary finishing tool member having conjugate teeth, rotating one of said members thereby driving the other memberthrough the intermeshing engagement'ef said teeth, the axes of said gear member and tgol member lying in no common plane and being crossed at an angle less than 25, feeding one of; said members relative to the other in the direction of the axis of said gear to be finished the finishing action and feeding one 6: said gears and contacting only that portion. er, the teeth of the finishing tool at the end thereof adjacent to said obstruction. 18. The method of finishing gears comprising mating the gear member t be finished with a. rotary finishing tool member having conjugate teeth, rotating one of said members thereby driving the other member through the intermeshing engagement of said 'teeth, the axes of said gear member and tool member lying in no common plane and being crossed at an angle less than '25" and said angle being slightly different than the angle causing correct meshing thereby causing greater finishing at the end portions of the teeth. 19. The rnethod of finishing gears'gcomprising mating the gear to be finished with a helical gear finishing tol having conjugate teeth, the axes of said gears; lying in no common plane and being rossed at an angle less than 25, rotating one of said gears thereby drivingv the other gear through the intermeshing engagement of said teeth, applying pressure to one of said gears to obtain pressure contact between the teeth during relative to the otherin the direction' oi the axis of said gear to be finished thereby extending the finishing action across the bearing face of the gear; i i 7 ROBERT ;S. DRUIVIMOND. my 

